First DSLR,noise on darks, blowed highlights...

Started Oct 1, 2020 | Discussions thread
bobn2 Forum Pro • Posts: 69,811
Re: First DSLR,noise on darks, blowed highlights...

kajaalyo wrote:


I have bought my first DSLR camera, Canon EOS 80D with EFS 18-55 1:3.5 - 5.6 IS STM lens.

My goal is to shoot car footage, but I feel that I must first master the photography.

I practiced for a few days with A+ auto mode, now I want to learn how to use manual mode.

I watched a few tutorials to get to know the things that I must adjust (shutter speed, ISO, f stop).

Now my problem is that when it`s starting to get dark, lets say 1.5hour before sundown or inside the house with normal lightning I start to get noise like on cheap digital camera from 2003 in low light.

I am aware that this could happen because of to much ISO, but I rather keep ISO low and I lower the shutter speed to compensate, but noise is still there.

My other problem is that I`m always blowing the highlights. It`s like I can`t drop down the ISO to make the sky darker or car reflections darker because everything on the picture will be too dark.

Do I need an ND filter or is there something that I can do to overcome this?

I had tried playing with shutter, iso and f stop to solve both of my problems, but I can`t figure it out.

It's frustrating when I know I had spend so much money and now iphone makes better pictures than 80D in my hands, if I dust of my note1 I bet, even that obsolete thing would take better pictures.

Thank you for help

You've got some good replies in this thread, from people who generally give good replies, so take some heed.

It's very hard for beginners to learn exposure technique, because something approaching 100% of easily accessible free web material on the topic is pure unadulterated nonsense, written by people who don't even know what exposure is. (Note: an exception to this is Richard Butler's articles on this site, which are well informed and not erroneous, if you want further information, go to them rather than random web-sites) When you do know what exposure is, and what 'ISO' is, it's quite simple, so I'll try to outline the basic principles. I apologise in advance for adding in a bit more technical detail than is strictly necessary, this is required to make things sufficiently unambiguous to withstand the inevitable pushback from people who have mislearned at the hands of the previously mentioned web sites.

First, what is 'exposure' The word 'exposure' in photography, in the context of camera settings, means the density (amount per unit area) of light energy at the sensor. The key thing to remember about exposure is the larger it is the better, since it is exposure that primarily determines how much noise there is in the image. You have perceptively noticed that the darker bits of your photo are noisier. That's because the exposure (light energy) in that part of the photo is low - because it's dark. In practice, exposure is set by three things.

The first is how much light is coming from the scene that you are photographing. This is technically called 'scene luminance'.

The second is the f-number that the lens is set to, where 'f-number' is the ratio of the focal length of the lens to its aperture (how big is the 'hole in the lens'). We use the f-number to set the aperture rather than the aperture directly because doing it this way automatically compensate for a wider angle of view collecting more light. If we didn't, our exposure calculations would need to take into account the angle of view of the lens we were using.

The third is the exposure time or 'shutter speed'. Together it and the f-number dictate how much of the light coming from the scene we collect.

So, now we've dealt with the controls, and said that we want to set the biggest exposure we can, we can see that means the largest aperture (smallest f-number) and longest exposure time (slowest shutter speed) possible. So the next question is, what stops us setting arbitrarily big apertures and slow shutter speeds?

The answer to that, is that these controls also affect aspects of our photos that we seek to control. The aperture, along with subject distance, controls the depth of field - how far into the scene is acceptably sharp. The larger the aperture the shallower our depth of field. So, in terms of managing exposure, we want to look for as shallow a depth of field as is acceptable. Many photographers end up using much smaller apertures than necessary, and thus get noisier images. There are several methods and rules of thumb for working out how much (or little) depth of field you actually need. One I often suggest was popularised by Harold Merklinger, and is good for landscapes. I find it quite easy to visualise what I want using this method. Look at the scene and decide what is the major subject you want to be sharp. That is where you will focus the camera. Now look at the foreground, and visualise how big is the actual size smallest feature you'l like to be rendered. For instance, if you have tree bark, you might think the 5mm will give a good rendering of the texture. Set your aperture to that. The f-number corresponding to that aperture is the focal length of your lens divided by the aperture you want. So if you decide that 5mm is the aperture you want and you have a 50mm lens, then you need an f-number of 10 (aperture is f/10). For portraiture and indoor shots, the old adage 'f/8 and be there' works quite well as a starting point, though you need to refactor the actual number for your camera - on yours f/5.6 would correspond to f/8 on a full-frame camera, for which the rule of thumb was formulated). You might find that larger apertures are useful to put the background out of focus.

Shutter speed is limited by your motion blur requirements. Camera shake damages photos more than a bit of noise, so best to avoid that rather than go for the bit of extra exposure. Again, there is a common rule of thumb, which is to set your shutter to at least the focal length of your lens, multiplied by 1.6 (again, a correction for the crop factor). If your lens has IS you can go slower than that. If you have a live subject,  you probably don't want to go much below 1/250 or 1/125. That is, unless you want to have intentional motion blur, which is a whole additional topic.

Setting exposure is really all about balancing noise against your requirements for DOF and motion blur.

Finally, onto ISO. This is one of the most misunderstood topics around exposure, and most web explainers on it are completely erroneous. ISO sets the relationship between the exposure of your shot and how light or dark the final image looks. This latter property is called the 'lightness'. Many photographers wrongly think it is called the 'exposure', which would leave 'ISO' setting the relationship between 'exposure' and 'exposure', an obvious nonsense. It is this failure to differentiate between what are two completely different things that renders most of the web explainers completely useless. You have picked up one of these bad ideas, that it is 'ISO' that causes noise. It is not, it is small exposures, it is just that you will use a high ISO with a small exposure to get it rendered with a good lightness. So, the final step in getting the right settings is to set the ISO to that needed to get a nice rendering of the exposure you have set. Your camera has an 'auto-ISO' setting that will do that. If you want to do it manually, just adjust the ISO until the meter is centred. If you can't get the ISO low enough to stop the meter showing over-exposure (+), then it means that your exposure is larger than the camera can physically accept. In that case simply reduce exposure by increasing the shutter speed (decreasing exposure time) or increasing the f-number (reducing the aperture) until the meter centres. Choose which one one the basis of whether you think you could do with more DOF or more resistance from motion blur.

Most exposure tutorials centre on setting exposure to get the lightness as you want, which ends up being very hard, which is why it's seen as such a black art. Generally the meter will give a good result, but if it doesn't it's not hard to tweak the lightness in processing, if you're shooting raw, or post-processing if you've shot JPEG. If you do it in processing, you have a lot of flexibility, because you're not trying to undo processing that has already occurred.

Just a not on your OP. Some scenes do include very bright highlights. ISO standards do include an allowance for this, but some scenes will exceed this. Often shooting in raw and processing for the highlights is a straightforward solution, because most cameras can accept more light than comes out 'white' in the JPEG. If not, then you can set the ISO a bit lower, to allow the camera to collect more light without saturating  - remembering that lightness can be set as you want or corrected, if in JPEG). If you're already down to the lowest ISO, then you'll need to back off the exposure a bit.

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